Study on the surface segregation of mixed ionic‐electronic conductor lanthanum‐based perovskite oxide La _1−x Sr _x Co _1−y Fe _y O _{3− δ} materials

Abstract

Summary High‐temperature solid oxide fuel cells (HT‐SOFCs) generally operate at 800°C to 1000°C and intermediate temperature SOFCs (IT‐SOFCs) at 600°C to 800°C. Reducing the SOFCs operational from high to ITs results in many issues mainly at the cathode site. One of the shortcomings that have been addressed is high polarization losses associated with oxygen reduction reaction (ORR) and degradation of La1−xSrxCo1−yFeyO3−δ (LSCF) cathode materials. Strontium (Sr) has been discovered to segregate and inhibit the surface‐active site for the ORR under specified conditions (temperature, relative humidity, and suppressing activity). It enriched the surface, formed Sr‐rich secondary phases, and eventually changes the composition and the structure of the perovskite surfaces. Therefore, this review aims to summarize the occurrences of Sr segregation at the LSCF cathode surfaces as a function of operating conditions and their effects on the material performance. In addition, the characterization techniques utilized to investigate the Sr segregation, and strategies for Sr segregation mitigation are also discussed.

Overview of Approaches to Increase the Electrochemical Activity of Conventional Perovskite Air Electrodes

“…However, these materials exhibit increased thermal and chemical expansion, which is detrimental to the long-term operation of SOFCs [33,34]. The poor long-term durability of high-temperature electrochemical cells is often caused by the performance degradation phenomenon of the air electrode [35][36][37]. It has been found that the electrochemical performance degradation of the LSM-and LSCF-based air electrodes may include microstructural coarsening [33,38,39], the electrolyte/cathode interface reactions [33,[40][41][42], sulfur [43][44][45] and chromium poisoning [44,[46][47][48][49], carbon deposition [50,51], and Sr surface segregation [33,35,36,52].…”

Advancements in Perovskite‐Based Cathode Materials for Solid Oxide Fuel Cells: A Comprehensive Review

“…Figure 11 illustrates SEM images of segregated strontium for LSCF based materials. [79] Furthermore, thermal stability of LSCF-based cathodes should also be considered in order to minimize degradation, stress, and their compatibility with other cell components under high operating temperature. As, Fe 3 + is found to have greater binding energy with oxygen as compared to Co 4 + .…”

Highly Stable Protonic Ceramic Electrolysis Cells Based on Air Electrodes with Finger-Like Pores Current Collection Layers Running in High-Steam-Content Air

“…Chemical stability is still a challenge for PCECs because the electrolysis operating conditions lead to exposure to an atmosphere containing a high steam content, in which the electrodes and electrolytes are thermodynamically unstable. , A high steam content of more than 40% is needed in the PCEC condition; the unreacted and remaining steam molecules in pores would cause a reduction in the length of the three-phase boundaries (TPBs) and higher polarization resistance. Besides, this residual vapor sometimes reacts with the electrolyte and produces an insulating secondary phase. , Therefore, chemically stable materials are needed in the air electrode, and increasing the electrode porosity and steam utilization factor is also considered to be another effective strategy. However, the simple addition of pore formers can no longer meet the porosity and microstructural requirements of air electrodes.…”